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| Titel |
Latitudinal and temporal distributions of diatom populations in the pelagic waters of the Subantarctic and Polar Frontal zones of the Southern Ocean and their role in the biological pump |
| VerfasserIn |
A. S. Rigual-Hernández, T. W. Trull, S. G. Bray, A. Cortina, L. K. Armand |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 12, no. 18 ; Nr. 12, no. 18 (2015-09-17), S.5309-5337 |
| Datensatznummer |
250118091
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| Publikation (Nr.) |
 copernicus.org/bg-12-5309-2015.pdf |
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| Zusammenfassung |
| The Subantarctic and Polar Frontal zones (SAZ and PFZ)
represent a large
portion of the total area of the Southern Ocean and serve as a strong sink
for atmospheric CO2. These regions are central to hypotheses linking
particle fluxes and climate change, yet multi-year records of modern flux
and the organisms that control it are, for obvious reasons, rare. In this
study, we examine two sediment trap records of the flux of diatoms and bulk
components collected by two bottom-tethered sediment traps deployed at
mesopelagic depths (~ 1 km) in the SAZ (2-year record; July
1999–October 2001) and in the PFZ (6-year record; September 1997–February 1998, July 1999–August 2000, November 2002–October 2004 and
December 2005–October 2007) along the 140° E meridian. These
traps provide a direct measure of transfer below winter mixed layer depths,
i.e. at depths where effective sequestration from the atmosphere occurs, in
contrast to study of processes in the surface ocean. Total mass fluxes were
about twofold higher in the PFZ (24 ± 13 g m−2 yr−1) than
in the SAZ (14 ± 2 g m−2 yr−1). Bulk chemical composition of
the particle fluxes mirrored the composition of the distinct plankton
communities of the surface layer, being dominated by carbonate in the SAZ
and by biogenic silica in the PFZ. Particulate organic carbon (POC) export was similar for the annual
average at both sites (1.0 ± 0.1 and 0.8 ± 0.4 g m−2 yr−1 for the PFZ and SAZ, respectively), indicating that the
particles in the SAZ were relatively POC rich. Seasonality in the particle
export was more pronounced in the PFZ. Peak fluxes occurred during summer in
the PFZ and during spring in the SAZ. The strong summer pulses in the PFZ
are responsible for a large fraction of the variability in carbon
sequestration from the atmosphere in this region. The latitudinal variation
of the total diatom flux was found to be in line with the biogenic silica
export with an annual flux of 31 ± 5.5 × 108 valves m−2 yr−1 at the PFZ compared to
0.5 ± 0.4 × 108 m−2 yr−1 at the SAZ. Fragilariopsis kerguelensis dominated the annual diatom export at both sites
(43 % at the SAZ and 59 % in the PFZ). POC fluxes displayed a strong
positive correlation with the relative contribution of a group of
weakly silicified and bloom-forming species in the PFZ. Several lines of
evidence suggests that the development of these species during the growth
season facilitates the formation of aggregates and carbon export. Our
results confirm previous work suggesting that F. kerguelensis plays a major role in the
decoupling of the carbon and silicon cycles in the high-nutrient
low-chlorophyll waters of the Southern Ocean. |
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